diff --git a/include/mapnik/expression_grammar_x3_def.hpp b/include/mapnik/expression_grammar_x3_def.hpp
index 690224b8f..7fb82a982 100644
--- a/include/mapnik/expression_grammar_x3_def.hpp
+++ b/include/mapnik/expression_grammar_x3_def.hpp
@@ -209,14 +209,17 @@ struct unary_function_types_ : x3::symbols<unary_function_impl>
 {
     unary_function_types_()
     {
-        add("sin", sin_impl())      //
-          ("cos", cos_impl())       //
-          ("tan", tan_impl())       //
-          ("atan", atan_impl())     //
-          ("exp", exp_impl())       //
-          ("log", log_impl())       //
-          ("abs", abs_impl())       //
-          ("length", length_impl()) //
+        add("sin", sin_impl())       //
+           ("cos", cos_impl())       //
+           ("tan", tan_impl())       //
+           ("atan", atan_impl())     //
+           ("exp", exp_impl())       //
+           ("log", log_impl())       //
+           ("abs", abs_impl())       //
+           ("length", length_impl()) //
+           ("int", int_impl())       //
+           ("float", float_impl())   //
+           ("str", str_impl())       //
           ;
     }
 } const unary_func_types;
diff --git a/include/mapnik/function_call.hpp b/include/mapnik/function_call.hpp
index 62e8a401d..91399e376 100644
--- a/include/mapnik/function_call.hpp
+++ b/include/mapnik/function_call.hpp
@@ -89,6 +89,25 @@ struct length_impl
     value_type operator()(value_type const& val) const { return val.to_unicode().length(); }
 };
 
+// str
+struct str_impl
+{
+    value_type operator()(value_type const& val) const { return val.to_unicode(); }
+};
+
+// int
+struct int_impl
+{
+    value_type operator()(value_type const& val) const { return val.to_int(); }
+};
+
+// float
+struct float_impl
+{
+    value_type operator()(value_type const& val) const { return val.to_double(); }
+};
+
+
 // min
 inline value_type min_impl(value_type const& arg1, value_type const& arg2)
 {